Protection against excessive voltages.



H. ENGEL.

PROTECTION AGAINST EXCESSIVE VOLTAGES.

APPLICATION FILED .IULY I4, I915.

1,266,434; Patented May14,1918.

WEI

Inventor: Hans En e I,

5 W MM H i sfittor'neg.

UNITED STATES PATENT OFFICE.

HANS ENGEL, OF CHARLOTTENBURG, GERMANY, ASSIGN OR TO GENERAL ELECTRIC 7 COMPANY, A CORPORATION OF NEW YORK.

PROTECTION AGAINST EXOESSIVE VOLTAGES.

Specification of Letters Patent.

Patented May 14, 1918.

Application filed July 14, 1915. Serial No. 39,900.

ject of the Emperor of Austria-Hungary,

residing at Charlottenburg, Germany, have invented certain new and useful Improvements in Protection Against Excessive Voltages, of which the following is a specification. I

My invention relates to the protection of electrical windings against excessive voltages,'and is especially useful for preventing current rushes and excessive voltages when transformers are connected to high voltage supply circuits. 7

In order that electrical windings, and particularly transformers, may be protected against surges when they are connected to high voltage supply circuits, it has been proposed to connect a protective resistance in series therewith before the connection to the supply circuit is altered, and to afterward short-circuit this resistance by contacts on the main switch. This need for protection is frequently encountered in electric railway work where temporary interruptionsof trolley voltage are not uncommon. In case of such an interruption, however, if the main switch should remain closed, all

protections would be lost upon the reappearance of trolley voltage, since the resistance would then be already short-circuited. This particular difliculty has been partially overcome in some cases byproviding a no-voltage release for the main switch. With this arrangement, it is found that the problem is still not wholly solved. In order to determine whether or not the trolley voltage has reappeared, the motorman mustthrow back his controller and attempt to close the switch. The switch will not stay closed, however, because of the no-voltage release and the motorman may have to try again and again before he will be successful. This involves a considerable loss of time, and where the time schedule is strict, as in the case of city express trains, it has been found that he will hold the main switch in by hand until trolley voltage appears. This results in impressing full voltage on the transformers without any protective resistance.

It is, accordingly, the object of my invention to provide a way in which these difficulties may be avoided. The manner in which this is accomplished will be more clearly understood by reference to the single diagrammatic figure of the accompanying drawing.

An electrical winding 10, in this case the primary winding of a transformer, is arranged to be connected, in series with a protective resistance 11, across a source of supply 12, by means of the switch 20. This switch, which is provided with contacts 21,

may be operated in any convenient manner, and it is here illustrated as operated" by means of a hand lever 22. For the purpose of making the protective resistance 11 ineffective after the winding 10 is energized, the switch 30 is arranged to short-circuit the same. This switch is provided with movable contacts 31, and is arranged to be operated automatically by an electromagnetic coil 32, which is here shown as energized from the secondary of the transformer 10. The switches 20 and 30 are shown as mechanically interlocked by means of the coacting arms 23 and 33 in such a way that the switch 30 can never be closed until after the switch 20 has been closed, and will always be opened before the switch 20 is opened. This is further aided by the design of the movable contacts 21 and 31, and it will be seen from an inspection of the drawing that the contacts 21 are longer than the contacts 31. It is desirable to provide some device whereby the closing of the switch 30 will be delayed a certain definite time after the closing of the switch 20, and this may conveniently be accomplished by means of a retarding device 34:. The switch 20 will preferably be provided with an overload trip latch 40, which is arranged to hold the switch closed against the force of gravity, and which may beremoved from its holding position by a trip coil L1 which may conveniently be energized from a current transformer 42 so that it will be responsive to the current flowing in the electrical winding 10. As an additional precaution, I have provided an interlock switch 43 upon the overload trip latch 40, so arranged that when the trip is operated, the coil 32 is deenergized. Thus, it will be seen that I have made doubly sure that the switch 30 shall open before the switch 20, first by denergizing the same, and then, in case of its failure to open by gravity, by so arranging the parts that it will be forced open by the'coaction of the arms23 and 33.

It will thus be seen that the difliculties previously discussed have been overcome,

and that a-protective resistance will always be placed in series with the winding which is to be protected before the connections to the source of supply are altered. In connecting the winding 10 to the source of supply, it will be seen that the switch 20 is first closed, and held in closed position by means of the latch 4L0, and that then, as soon as the winding 10 is energized by having been connected to the source through thel'resistance 11, said resistance will be. renderedineffective by being short-circuited by means of the switch 30, which will be closed by the energization of the coil 32. In case of a failure of trolley voltage, the coil 32 will be deenergized, and the switch 30 will be opened, so that the protective resistance 11 is at once placed in circuit with the wind ing 10. Upon the reappearance of trolley voltage, full protection will be obtained,

and, after a lapse of a definite time, determined by the retarding device 34, the switch 30 will be closed, to short-circuit the resistance. The switch 20 may be opened by manually tripping the latch 4:0, or this latch may be tripped because of an overload. In either case it will be seen that the winding 32 is first denergized to allow the switch 30 to open by gravity, and that then the switch 20 will open by gravity and by reason of the coaction of the arms 23 and 33, and by the relation of the lengths of'the switch contacts 21 and 31, the switch 30 will be positively opened before the switch 20.

I wish it understood that while my invention extends to all the details of the arrangement which has been shown and, described, I seek to cover in the appended claims all such obvious modifications thereof as come within the true scope and spirit of my invention. I

WhatI claim as new and desire to secure by Letters Patent of the United States, is,-

1. In combination, a source of supply, a protective resistance, an electrical winding, a switching device arranged to connect said resistance and said winding in series across said source, and automatic means dependent upon both the voltage on and current in said winding for rendering said resistance inel fective.

2. In combination, a source of supply, a protective resistance, an electrical winding, a switching device arranged to connect said resistance and winding in series across said source, and electromagnetic means operable upon the energization of said winding for short-circuiting said resistance.

3. In combination, a source of supply, a protective resistance, an electrical winding, a

switching device arranged. to connect said resistance andwinding in series across said source, and electromagnetic means responslve to the voltage on sa1d winding for short circuiting said resistance, said switching device and said electromagnetic means being mechanically interlocked, so that the latter is opened before the former.

i. In combination, a source of supply, an electrical winding, a protective resistance, a

switching device adapted when in its closed position to complete a circuit through said source, said winding, and said protective resistance, and adapted when in its open posi tion to interrupt said circuit, automatic means responsive to the voltage on said winding for rendering said resistance; ineffective, said switching device and; said automatic means beingmechanically interlocked so that the resistance can be rendered ineffective only after the switching device, is moved to its closed position.

5. In combination, a source of supply, an electrical winding, a protective resistance, a switching device adapted when in its closed position to complete a circuit through said source, said winding and said resistance, and

adapted when in its openposition to interswitching device is moved to its closed position and so that the switching device can be moved to its open position only after the resistance is rendered effective.

6. In combination, a source of supply, an electrical winding a protective resistance, a

switching device adapted when in its closed,

position to complete a circuit through said source, said winding, and said protective resistance, and adapted when in its open posi tion to interrupt said circuit, electro-magnetic means responsive to the voltage on said winding for rendering said resistance ineffective, means for maintaining said switching device in its closed position, and-means responsive to an overload current in said winding. to cause the opening of said switching device and the deenergization of said electro-magnetic means, said switching device and said electro-magneticmeansbeing mechanically interlocked so that the resistance can be rendered ineffective only after the switching device is moved to its closed position andso that the switchingdevice can be moved to its open position only after the resistance is rendered inefi'ective.

7 In combination, 'a source of supply,ua protective resistance, an electrical winding, a switching device arranged to connect said resistance and winding in seriesacross-said source, electromagnetic means responsive to the voltage on said winding for short-circuiting said resistance, and means responsive the voltage on said winding for short-cirto the current in said Winding controlling cuiting said resistance, and an overload trip 10 the circuit of said electromagnetic means. latch for said switching device combined 8. In combination, a source of supply, a with means controlling the circuit of said 5 protective resistance, an electrical winding, electromagnetic means.

a switching device arranged to connect said In witness whereof, I have hereunto set resistance and winding in series across said my hand this 5th day of June, 1915. source, electromagnetic means responsive to HANS ENGEL.

copies of this patent may be obtained for five cents each, by addressing the "Commissioner of ratents, Washington, D. G. 

